After being rolled to a certain thickness by a cold rolling machine, the strip steel, depending upon the demands of products, will be transferred into some different post-processing processes, for instance, hot dip galvanized products need to be transferred into the continuous galvanizing units, electrogalvanized products need to be transferred into continuous electrogalvanizing units after continuous annealing, and the common cold products forms cold rolled products through the continuous annealing process or the batch annealing process. For the strip steel coating process such as the continuous hot dip galvanizing or the electrogalvanizing process, the surface condition and the cleanliness of the strip is the prerequisite to ensure the quality of the continuous annealed coatings. However, during rolling the strip, it is difficult to prevent various foreign materials, such as dregs in the rolling oil, residual iron powder in cold rolling, accumulating dust, weld slag produced in head welding or the like, from remaining on the surfaces thereof.
Consequently, the strip has to be cleaned so as to remove thoroughly the oil contaminations on its surface before continuous annealing. Otherwise, a variety of oils remaining on the surfaces would form carbonaceous blotches during annealing, which will contaminate the atmosphere inside the furnace, affect the efficiency of decarburization, and even cause recarburization. Additionally, the oil contaminations may change the quality of the strip surfaces and induce nodulation on the bottom rollers, thereby resulting in defects such as surface scratches thereof, or the like.
In light of this, a rinsing process is provided on the continuous coating units before annealing, which process is also referred to as degreasing process, with the aim of removing the variety of foreign materials residual on the strip surfaces.
For the continuous annealing process after which cold rolled products are directly formed, the surface cleanliness of the incoming strips determines directly the surface quality of the final products. In view of this, surface pre-treatment processes such as alkaline washing, brush washing, electrolysis washing, hot water rinsing or the like, are provided on the entry section of the continuous annealing processing line, so as to ensure the surface quality of the strips entering there. Similarly, in the batch annealing process, specific degreasing devices are disposed before the batch annealing processing line, so as to guarantee the surface quality of the strips entering there.
However, in the practical manufacturing process, there are always such phenomena that dirty matters on the strip surfaces that cannot be cleared away, causing spots, stripes, uneven coats to occur on the surfaces after the strips are subjected to annealing or coating, so that the surface quality of the products would be influenced. To overcome these, the skilled in the site provide many adjustments and optimization on the aspects of the processes, such as alkaline spraying process, brush washing process, degreasers, lye concentration, and temperature. Nevertheless, owing to the variety and complexity of the dirty matters, such as the difference in components between different strips, the inconformity of the bonding force between the matters and the strips, and the rapid running of the strips, the dirty matters on the strip surfaces cannot yet be cleared away thorough during manufacturing.
Additionally, to meet the requirements for the roughness and the following coating process by customers, it is necessary for the surfaces of the cold rolled strip to be of a certain roughness, but due to the limitations on the rolling process and the rollers, the roughness thereof cannot meet the requirements often. Especially when manufacturing the high-strength steels with high intensity, the surface roughness thereof cannot reach the standard, even if the roughness controlling ability of the roll machine reaches to the extremity.
In light of this, it is necessary to control the roughness of the strips during the procedures following the cold rolling process, wherein only the skin-pass mill can control the surface roughness of the strips. However, there are a lot of problems with the roughness control during the skin pass process, for instance,
1) during the skin pass process, the roughness of the work rollers have the maximum effect on the surface roughness of the strip. The work rollers should be treated prior to working, by laser texturing, electric spark texturing, shot blasting or the like, so as to impart the surface of the work rollers a certain roughness. In the beginning of the period when the work roller work, the surface roughness of the roller surfaces is the key factors to determine the surface roughness of the strips. Nevertheless, with the increase of the rolling mileages, the surface roughness of the roller decreases, causing the surface roughness of the strip to be unable to meet the requirement of the customer;
2) during the skin pass process, due to that controlling the surface roughness of the rollers is the only method of controlling the roughness of the strips, when the roughness of finished products are found not meeting the requirement, the only way is to replace the rollers, whereby the roughness thereof cannot be flexibly controlled.
3) with the increase on the requirement of the high strength steels, the strength of the strip becomes higher, and if the strength thereof reaches a certain level, the requirements of customers may not be met by the skin-pass mill, even when the rollers just begin to work.
Consequently, it is badly in need to develop processes and equipments for controlling the surface roughness of the strips.
Aiming to the problems on the pre-treatment and roughness of the rolled strip surfaces, a large amount of researches have been carried out in and out of the country. For instance, a high density current degreasing technique is developed abroad for the pre-treatment on the surface of the strips, the principle of which is to take alkaline degreasing liquid as the conduct medium to form a high density of current of about 200 A/d m2 on the strip surfaces, such that a large amount of bubbles are generated in an instant on the strip surfaces to blast the layer of the oil contaminations thereon, thereby cleaning the strips. Although this technique can be adapted to the rapid manufacturing, it would consume the electric energy as 10 times as the traditional processes, and its production cost is very high; additionally, due to it is of high precision, the maintenance cost thereof is also very high. The China patent CN102357541A discloses a method of washing the strip surface with hot water circulation, and a system thereof. Its principle is that before the strips are subjected to alkaline brush washing, hot water with a high pressure of 8˜12 MPa and a temperature of 40˜70° C., is used to spray onto the upper and lower surfaces of the strip, so as to reduce the number of the combination equipments and the energy consumption during the subsequent alkaline brush washing and electrolysis procedures. This method acts as an improved one of the traditional degreasing process. The way of spraying hot water can wash away those foreign materials weakly bonding to the strip surface, but cannot clear thoroughly those tightly bonding to the strips and those recessed in the dent layers thereof. China patent CN201217016 Y discloses an ultrasonic treatment device for washing the strip surface, the principle of which is to combine the strip surface washing process with the ultrasonic treatment, and additionally install a ultrasonic wave generation device into the strip alkaline washing (pickling) or electrolysis alkaline washing (pickling) sink, so as to wash and clean the strip surfaces. This method also acts as an improved one of the traditional degreasing process, which improves the flow of alkaline liquid, that is, has an obvious effect on removing the oil film of the strip surface, but cannot yet clear away thoroughly the foreign materials bonding tightly to the strips. China patent CN101537431A introduces a method of online predicting and controlling the surface roughness of thin strips, which is characterized in that the roughness values in different length of the strips are calculated by the roughness data of the work rollers of the skin-pass mill, the length of the strip, the rolling force in different lengths of strips, and the elongation rate thereof, and when the target value of the roughness of the strip does not fall into the predicted scopes, the roughness is predicted and controlled by adjusting the rolling force and the elongation rate. This method can only reduce the roughness errors of the strip, but unable to solve the problem that the roughness cannot reach the standard in the traditional process. The patent CN1804739A introduces a technology for predicting and controlling the surface roughness of finished plate for skin-pass mill, the principle of which goes similarly to the above-mentioned patent, that is, to predict and control the surface roughness of strip by building a mathematic model between the roller roughness and rolling kilograms, and a mathematic relationship between the reduction rate and heritability, and by building a model of skin-pass mill online predicting finished products roughness according to the site data. Similarly, this method can only reduce the roughness errors of the strips, but unable solve the problem that the roughness cannot reach the standard in the traditional process.
The patent CN101675184A discloses a steel sheet rinsing method for rinsing a running steel sheet, and a steel sheet continuous rinsing apparatus, the principle of which is to supply the ultrasonic washing liquid with a frequency of 0.8 MHz˜3 MHz to the steel sheet surface inclined by an angle of 1˜80° relative to a line perpendicular to the steel sheet surface along a direction opposite to the running direction of the steel sheet in a spraying manner or a curtain manner, whereby the high frequency ultrasonic wave is utilized for rinsing the surfaces of the running steel sheets, and the rinsing effect and the rinsing speed is improved. This method adopts the cavitation occurring on the steel sheet to intensify the chemical reaction of the rinsing, and provide the impact force, thereby enhancing the rinsing effect, but it is yet unable to clear away the foreign materials bonding tightly to the strip. Aiming to control of the surface roughness of the strip, the patent CN1622869A owned to a Japanese applicant introduces a surface treatment facility of metal plate and a method for producing metal plate, which features in that the surface roughness of the steel sheet is controlled by blasting solid particles having an average particle diameter 300 μm onto the metal plate which is continuously transferred. The present invention consists mainly of a blasting chamber in which a blasting device is disposed, and cleaning means provided at the downstream of the blasting chamber for cleaning the surface of the metal sheet. Specifically, a metal plate enters the blasting chamber wherein the blasting device impacts the dry solid particles onto the surface thereof, and the cleaning chamber at the downstream of the blasting chamber rinses the solid particles on the surface of the metal plate by means of air nozzles. In this invention, the medium for impacting the strip surfaces is dry solid particles, which may result in that the metal plate entering the blasting chamber is required to be dry for keeping the mobility of the solid particles. Consequently, it is necessary to provide devices for rinsing and drying the steel sheet on the blasting chamber, which may lead to complicated units. Additionally, during the whole blasting and rinsing process, no liquid should be accessible to the units, which is a high requirement on sealing the devices and the like, that is difficult to meet in actual production. Furthermore, the solid particles are impacted directly onto the surface of the metal plate, and owing to that the particle size of the solid particles are larger than that of the metal plate, the solid particles are apt to embedding into the metal plate surface and hence the solid particles on the strip surfaces cannot be cleared away thoroughly by spraying air in this invention.